CLIMATE IMPACTS ON NITRATE LOSS IN DRAINAGE WATERS FROM A SOUTHERN ALLUVIAL SOIL

Abstract

Fertilizer nitrogen transported via agricultural drainage has caused eutrophication of nearby surface waters. Inthe Lower Mississippi River Valley region, periods of drought are occurring more frequently. The impacts of drought on nutrientloss from agricultural lands of this region have not been reported. Field studies were used to evaluate the impact of climate (rainfall)on nitrate loss from agricultural fields in both normal (1996) and drought (1999) periods at the Ben Hur Water QualitySite in Baton Rouge, Louisiana. Four replicates of two treatments, surface drainage only (SUR) and surface drainage + deepcontrolled drainage (DCD), were initiated on 0.21 ha plots planted to corn (Zea mays L.). After each rainfall/runoff event, thevolumes of runoff and subsurface drainage were analyzed for soluble nitrate concentration and loss. No significant drainagetreatment impacts were found on runoff volume and nitrate loss in runoff. Nitrate loss in runoff was impacted by climate, witha four-fold decrease in nitrate loss during the drought, caused by decreased volume of runoff. Conversely, the mass of nitrateloss in leachate increased two-fold during the drought. Diverting subsurface drainage effluent (DCD) to surface receivingwaters increased nitrate transport to these waters by 2.6 times in the normal climate, and over ten-fold during the drought,compared to SUR management. In either climate, but particularly during drought, subsurface drainage could potentiallyaccelerate eutrophication of receiving waters of this region. When compared to DCD, these results suggest that SUR should bethe water management practice in this region.